1. Field of the Invention
The present invention relates to a color image sensor in which five or more kinds of color filters are arranged in front of an image pickup device, and to an apparatus which performs a demosaicing process to obtained mosaic image data by using the color image sensor in which the five or more kinds of color filters are arranged in front of the image pickup device.
2. Description of the Related Art
In an apparatus such as a digital camera, a digital video camera or the like which inputs an color image, a single-chip color image sensor which uses a solid-state image sensing device such as a CCD (charge coupled device), a CMOS (complementary metal-oxide semiconductor) sensor or the like is used in a general way. Further, in the apparatus like this, color filters which respectively have different characteristics of spectral transmittance are arranged in front of the solid-state image sensing device, whereby color information according to input light is generated. Generally, in the apparatus like this, the color filters which have spectral transmittances respectively corresponding to red (R), green (G) and blue (B) are periodically arranged at a rate of R:G:B=1:2:1 with respect to every 2×2 pixels (for example, U.S. Pat. No. 5,373,322).
Incidentally, an image which is output from the single-chip color image sensor like this is a so-called mosaic image which has only single color information with respect to each pixel. For this reason, other color information which is lacking in each of the pixels constituting the mosaic image is generated by performing interpolation based on the color information of other pixels (hereinafter, called demosaicing), whereby the color information of each of R, G and B is generated with respect to one pixel. In any case, as a method of performing the demosaicing, there is widely known a method of performing, to obtain other color information which cannot be obtained in each pixel, spatial interpolation based on color information of environmental pixels (for example, Japanese Patent Application Laid-Open No. 2003-087806).
On one hand, there is a camera which is called a multiband camera. The multiband camera aims to reproduce spectral information of a subject by using plural kinds of color filters. For this reason, the multiband camera improves reproduction accuracy of the spectral information by increasing the number of kinds of color filters which respectively have different peak wavelengths of spectral transmittances and different full widths at half maximum.
In a single-chip multiband camera in which color filters are arranged in front of a solid-state image sensing device, it is necessary to provide and arrange plural kinds of color filters in front of the solid-state image sensing device. For example, as a multiband camera in which five or more kinds of color filters are arranged on one solid-stage image sensing device, there is known a multiband camera in which color filters are vorticosely arranged in order of peak wavelength.
In a case where the color filters are vorticosely arranged, satisfactory demosaicing can be performed by using peripheral pixel information in an area where the color filters having adjacent peak wavelengths are adjacent to each other. However, in areas other than the area where the color filters having the adjacent peak wavelengths are adjacent to each other, color filters having adjacent peak wavelengths are not adjacent to each other. For this reason, in the case where demosaicing is performed, if an image which has a high spatial frequency is input, a color which is called a false color different from an original color is reproduced. As a result, a spatial frequency (i.e., definition or resolution) which can be accurately resolved deteriorates.
Further, the method disclosed in Japanese Patent Application Laid-Open No. 2003-087806 premises that three kinds of color filters, i.e., R, G and B filters, are used. Consequently, if the number of kinds of color filters to be used increases, it is impossible to prevent deterioration of the definition due to the demosaicing.